Neutral metal cleaning compositions containing hydrazine and a polycarboxylamino acid



United. 31 States Patent T Edgar Ct Pitzer, Scotia,.N.Y., assignor tothe United States of Americans represented by the United States AtomicEnergy Commission No Drawing. Filed June 17, 19.64, Ser. No. 375,985

10. Claims. (Cl. 252-142) This invention relates to chemicalcompositions and a process for the removal of corrosion products frommetal surfaces? substantially neutral chemical compositions and theprocess: of employing them for the removal of oxide films fromiron andferrous alloys in inaccessible places.

Removalof oxide corrosion products from metal surfaces:;may beaccomplished by several physical or chemicalmeans; Scraping,sandblasting, pickling, and reduction are exemplary of a few of the wellknown cleaning methods which may be used. All of these methods may beeasily employed with no particular problem when the metal surfaces areexposed and accessible. However, when corrosion or crud removal frominaccessible metal interiors is necessary, application of phyicalremoval means isimpossible and resort to chemical compositions mustbe-taken.:

In. the past, the chemical compositions which were employed for crud andcorrosion removal were either strongly acidic. or strongly basic andrequired special precautionary -measures for handling and application.Moreover; application of solutions in the extreme pH ranges etchedhighly finished metal surfaces so that previously close .fittingtolerances were ruined, and even then, dissolution of all theobjectionable oxides forming the crud was not always effected.Particularly resistant to dissolution .was magnetic iron oxide.

Certain: of the metal cleaning chemical compositions inthe prior artcontained sulfur compounds. These compositions, while acceptable forcertain applications, were objectionable for apparatus constructed fromexpensive alloys which were subject to abnormal stresses. Sulfiteembrit-tlement or crevice. corrosion resulting from attack on 31116metal surfaces by the sulfur compounds produced equipment havingunsatisfactory strength and reliability. Often, as a result of the useof these sulfur containing compositions, the cleaned product wasstructurally more unsatisfactory than the corroded metal.

The primary object. of this invention, therefore, is to provide tsubstantially neutral metal cleaning compositions; which Ilwill removeall objectionable metallic oxide filmsvwithout etching the surface.

A furtherobject of this invention is to provide a safe, substantiallyneutral metal cleaning composition having a pH range of between 6.5 and9.5.

An additional object of this invention is to provide neutral metalcleaning compositions which will effectively clean .-a wide variety ofstructural metals and alloys.

Further; objects will become apparent to those skilled in the art fromthe following explanation and examples.

The foregoing objects are achieved according to this invention wbyformulating buffered aqueous solutions of hydrazine: and apolycarboxylamine acid chelating agent.

. Chelating agentswhichjcontain 3 to 5 carboxyl groups appear toheroughly equivalent in this solution. Exemplarypolycarboxylamine acidswhich are equivalent constitutents of: these novel cleaning compositionsare nitrolotriacetic acid, N- hydroxyethylethylenediaminetriacetic acid,diethylenetriaminepentaacetic acid, and1,2-diaminocyclohexanetetraacetic acid; however,ethylenediaminetetraacetic. acid is preferred. No sulfur compounds orMore particularly, this invention relates' to 3,297,580 Patented Jan.10, 1967 other constituents leading to sulfite embrittlement, crevicecorrosion, or other mishap are present in the ingredients. The metalcleaning composition according to this invention is non-corrosive to allferrous metals and alloys.

Hydrazine, alone, or the metal salts of the polycarboxylamino acids inthe absence of hydrazine have no appreciable effect upon certain mixedmetal oxides, that is, oxides of iron, cobalt, nickel, and manganese. Asynergistic action, evidenced by the unexpected improved solubility ofthe metal axides, occurs when the two compounds are mixed in the properproportions. This synergistic action dissolves metal oxides which weresubstantially immune to the separate ingredients-Ethylenediaminetetraacetic acid (EDTA) is mixed '7 with hydrazine inproportions which will result in a pH of from 6.5 to 9.5 and preferablyin a range of 7 to 9. Ammonia may be substituted as a buffering agentfor a portion of the hydrazine when it is necessary to adjust the pH ofthe resulting solution to bring it within the desired range. Theproportions of hydrazine and ethylenediaminetetraacetic acid are notcritical provided at least 0.1 molar concentration of hydrazine is usedand the pH remains within the prescribed range. Generally, a ratio of 2to 6 moles of hydrazine per mole of ethylenediaminetetraacetic acid willkeep the cleaning solution within the prescribed pH range. However, ifthe proportions of the ingredients render the pH of the solution belowthe 6.5 to 9.5 range, ammonia may be added to make the necessaryadjustments in the pH.

The minimum concentration of ethylenediamineteteraaceti acid which iseffectively used must be at least 0.08 molar; however, a concentrationof 0.25 molar is preferred. The concentration of hydrazine used with theethylenediaminetetraacetic acid has li tle consequence on theeffectiveness of the solution, provided the solution is at least 0.1molar in hydrazine.

Dissolution of metal corrosion products is better effected the cleaningsolution is employed at elevated temperatures. Dissolution of magneticiron oxide (E2 0 may normally be achieved in approximately two hourswith the solution at 95 to 100 C.; however, significant dissolution maybe effected after a one hour application at temperatures between and 100C. Although dissolution has been detected at temperatures as low as 65C., in order to maintain a rapid reaction, temperatures in the range ofto 100 C. are preferred.

EXAMPLE I Several samples were prepared in which the hydrazineconcentration in the cleaning solution was varied from 0.1 to 0.5 molar.Ammonia was added to the solution in amounts sufl'icient to bring the pHwithin the 6.5 to 9.5 range. A blue or greenish blue coloration upon theaddition of bromthymol indicator denoted the proper pH of the solution.

Approximately 0.2 gram of magnetic iron oxide (Fe O was added to each ofthe various concentrations and heated for two hours at C. An examinationof the various samples after completion of the treatment showed that thesolutions 0.2 to 0.5 molar in hydrazine dissolved 99.9% of the magneticiron oxide. The solution 0.1 molar in hydrazine dissolved 99.7% of themagnetic iron oxide.

Example II Additional samples were prepared to determine the effect ofthe hydrazine-EDTA solution on oxides of mixed metals, particularly,oxides of iron, nickel, cobalt, and manganese. Separate samples of thesemixed metal oxides were heated to 400 C. and to 600 C. The compositionof the metals oxides was determined by X-ray fluorescent analysis tocontain 76% Fe, 7.2% Ni, 8.4% Co, and

8.4% Mn. Samples of these mixed oxides were heated for two hours at 95C. in a solution 0.1 molar in ethylenediaminetetraacetic acid and 0.5molar in hydrazine. Approximately 91.8% of the mixed oxides which wereheated to 400 C. were dissolved in the solution. The mixed metal oxideswhich were heated to 600 C. were slightly more resistant to dissolutionin the same composition than the ones heated to 400 C. About 76.5% ofthe mixed metal oxides which were heated to 600 C. were dissolved in thesolution. An analysis of the mixed metal oxide residue showed thatapproximately 95.0% of the iron oxide, 87% f the nickel oxide, 89% ofthe cobalt oxide, and 57% of the manganese oxide in the original samplewere dissolved.

The test conditions under which this solution was tested were moresevere than normally encountered. Normally, the corrosion products ofmetal alloys are not exposed to temperatures as high at 400 C. to 600 C.These conditions are far more severe than those in which the solution isnormally applied.

Example 111 Several more samples were prepared using a hydrazine- EDTAsolution of the same formulation as in Example II. Radioactive oxidecorrosion products scraped from a nuclear reactor fuel element wereplaced in the solution and heated at 95 for 4 hours. The resultsobtained from the test are summarized in the following table:

Iron, nickel, and cobalt oxides showed satisfactory solubility whilechromium remained unaffected by the solution.

Example IV Other samples were prepared for the purpose of determiningthe solubility of magnetic iron oxide in a solution containing hydrazineand a different chelating agent. A solution containing hydrazine andnitrilotriacetic acid (NTA) was prepared. Weighted samples of magneticiron oxide were placed in portions of the neutral solution and heated to95 C. for 2 hours. The following table summarizes the results obtainedfor the test.

TABLE II Undis- N TA Hydrazine pH pH solved (molar) (molar) InitiallyFinally Residue,

Percent Similar results were obtained with solutions containing ammoniaas partial replacement for hydrazine. Solutions in which the pH wasadjusted by an ammonia bufier, meantime taking care to maintain at leastan 0.3 molar concentration of hydrazine in the solution, hadsubstantially no detrimental effect on the dissolving power of thesolution, and residues comparable to those shown in Table II wereproduced.

Example V The hyd-razine-EDTA solution, according to this invention, wasemployed in the decontamination of a primary loop pressurizer in apressurized water reactor cooling system. The initial dose rate in thepressurizer averaged approximately 1,0 00 to 1,200 mirlliroentgens perhour. One application of the hydrazine-EDTA solution produced adecontamination factor of from 2 to 5. The decontamination factor isdefined as the initial dose rate divided by the final dose rate.Outstanding decontamination was achieved by an additional treatment withpotassium permanganate followed by a second hydrazine- EDTA application.This three-step process reduced the initial average dose to an averageof approximately 5 milliroentgens per hour, giving a decontaminationfactor range from 400 to 900. In order to appreciate the benefits andadvantages 0 fthis neutral hydrazine-chelate solution, and theimprovements which it makes over the prior art, comparisons were madebetween prior art compositions and the hydrazine-EDTA solution.

Example VI Magnetic iron oxide (Fe O pellets were placed in testsolutions and all of the samples were heated for one hour at C. Oxalicand citric acids and their salts were compared with hydrazine-EDTA, asshown in the following table.

TABLE III Undissolved Compounds Molar pH Residue,

Percent 0. 25 0. 99 48. 4 0. 25 1. 61 91. 6 0. 20 4. 75 81. 3 0. 20 0.50 Ammonia 0. 60 8. 55 0. 92

It is evident from an observation of the amount of the residues thatsalts of these carboxylic acids commonly used in descaling solutionswere not nearly as effective as the hydrazine-EDTA solution.

From the afore-disclosed examples, it can be seen that the neutralhydrazine-EDTA solution according to this invention offers numerousadvantages over the prior art cleaning compositions. The solution is, ofcourse, attractive not only from the standpoint of being effective inthe removal of corrosion products which are only partially dissolved orremoved by prior art compositions, but also from the sandpoint of beingcompletely safe with respect to the personnel handling the solution, dueto its neutral or nearly neutral pH.

It is to be understood that certain changes and modifications can beperformed on the composition disclosed herein without departing from thespirit and scope of the invention. Having thus described my invention, Iclaim:

1. A substantially neutral metal cleaning composition consistingessentially of an aqueous solution of hydrazine and a polycarboxylarninoacid having 3 to 5 carboxyl groups in proportions yielding a solutionhaving a pH between 6.5 to 9.5 and wherein the concentration ofhydrazine is from 0.1 molar to 0.5 molar.

2. A substantially neutral metal cleaning composition a/ccorging toclaim 1 wherein the pH of the solution is 3. A substantially neutralmetal cleaning composition according to claim 1 wherein thepolycarboxylamino acid is ethylenediaminetetraacetic acid.

4. A substantially neutral metal cleaning composition according to claim1 wherein the polycarboxylamino acid is nitrilotriacetic acid.

5. A substantially neutral metal cleaning composition according to claim1 wherein the polycarboxylamino acid isN-hydroxyethylethylenediaminetriacetic acid,

7. A substantially neutral metal cleaning composition according toclaim, 1 wherein the polycarboxylarnino acid iss:1,2diarninocyclohexanetetraacetic acid.

8. .A substantially neutral metal cleaning composition according toclaim 1 wherein the proportions are 2 to 6 molesiof hydrazine per moleof polycarboxylamino acid.

9. A substantially neutral metal cleaning composition according to claim1 wherein the concentration of the polycarboxylamino acid is from 0.08molar to 0.25 molar.

10. 11A substantially neutral metal cleaning composition 1 according toclaim 1 wherein a portion of the hydrazine isreplaced by ammonia.

6.i=A"su'bstantial1y neutral metal cleaning composition according toclaim 1 wherein the polycarboxylamino acid isdiethylenetriaminepentaacetic acid.

References Cited by the Examiner UNITED STATES PATENTS 2,908,547 10/1959Nicholls et a1. 23-339 3,054,746 9/1962 Gaden et a']. 25230l.1 3,054,7479/1962 Gaden et a1. 25230l.l 3,154,500 10/1964 Jansen et a1. 252-6011CARL D. QUARFORTH, Primary Examiner.

S. I. LECHERT, JR., Assistant Examiner.

1. A SUBSTANTIALLY NEUTRAL METAL CLEANING COMPOSITION CONSISTINGESSENTIALLY OF AN AQUEOUS SOLUTION OF HYDRAZINE AND A POLYCARBOXYLAMINOACID HAVING 3 TO 5 CARBOXYL GROUPS IN PROPORTIONS YIELDING A SOLUTIONHAVING A PH BETWEEN 6.5 TO 9.5 AND WHEREIN THE CONCENTRATION OFHYDRAZINE IS FROM 0.1 MOLAR TO 0.5 MOLAR.